Lacecap Hydrangea or Hydrangea macrophylla, a species of plants from the Hydrangeaceae family is indigenous to Japan, growing in seaside as well as mountainous habitats. It is extensively cultivated in several areas over the world, under many different climates, becoming naturalized in China, the Americas, and New Zealand, and has become invasive in the Madeira and Azores archipelagos.
This deciduous shrub grows to mature dimensions ranging from 6 – 10 feet tall with a width of 8 feet. The green opposite leaves are 6 inches long with largely serrated edges. The flowering season lasts from early summer to late autumn.
The flowers form flattened clusters of blue, pink, red, light, or dark purple, consisting of arrangements of big, showy, infertile florets around a center of smaller fertile flowers creating a “lacy” appearance. The flower colors produced depend on the pH of the soil they grow in – acidic soil results in blue flowers, whereas alkaline soil results in pink flowers.
This color change in flower pigments is due to aluminum ions which are taken up by hyper-accumulating plants. The fruit is a somewhat globe-shaped capsule.
This plant does well in a border of mixed shrubs or at the rear of flower beds, with large size and rich foliage making it a delightful background for white or lighter colored flowers. This plant adds a lovely splash of early summer colors in shaded areas or woodland gardens in warm climates.
This plant grows best if planted in a spot that gets sun in the mornings and shade in the afternoons. It is an easy plant to maintain when its lighting needs are met. While it enjoys sunshine, too much exposure to direct sun will make the soil overheat, stress the plant, and cause it to wilt.
This plant needs regular watering without getting water-logged, so the soil it grows in should drain well yet stay slightly damp between watering. It will suffer damage in soggy soil.
This plant needs average to high humidity. Dry air in winter can cause it to wilt and suffer damage. Protect it from hot or cold drafts.
The hardiness zones for this plant are 6 – 9. While it is supposed to withstand temperatures of -10℉, freezing temperatures in late autumn or spring might affect the flowering ability of the plant a high summer temperature of 86°F or more will stress the plant and cause it to wilt.
This plant requires rich, well-draining yet moist soil amended with organic compost or manure. Mulching will help the soil retain moisture and keep the roots cool in hot summers but don’t allow the mulch to touch the stems.
This plant should be repotted after it outgrows the current container. Since it grows rather tall, ultimately fully mature plants will need its final container to be around the size of half a whiskey barrel. When repotting, always use fresh soil with regular watering – perhaps a bit more frequently than plants growing outdoors in gardens since container plants tend to dry faster. Most potted plants die from a lack of water.
This plant can be propagated during its growing season, cutting 2 or 3 6-inch long sections into a healthy stem to verify that every cutting has a leaf node at the bottom, remove the leaves except at the top and cut the leaves that remain in half, and place all the cuttings into water.
Fill a container with rich potting soil, and water well, allowing the water to drain out and make holes in the soil with a finger. Dust the cuttings with rooting powder, if desired push the cuttings about 3 inches into the soil and tamp the soil down.
Cover with plastic film to retain water, keep the plastic from contacting the cuttings with wooden sticks, place the container under indirect bright sunlight, remove the plastic every day and inspect the cuttings and soil for diseases or pests, removing any cuttings with signs of infection/infestation. Mist the soil if it is dry and cover again.
Rooting will generally take about four weeks, to uncover the container and allow the cuttings to grow and develop a vigorous root system. Transplant the cuttings into slightly bigger containers until the new plants are large enough to transfer into the garden or a larger container.
Fertilizer will help boost the growth of this plant. Apply balanced fertilizer or blend in organic compost with the soil in spring every year, but don’t feed it after August as the plant will become dormant in winter, with frost damaging any new growth that emerges.
Regular pruning isn’t recommended although this plant will tolerate pruning when necessary. Removing old damaged, dead or wayward growth is best done after the flowering season. While this plant isn’t a particularly difficult plant to maintain, it might not flower due to damage from cold winters, insufficient sunlight, excessive nitrogen, or pruning it during the wrong time which can remove flower buds. As mentioned, pruning is best done when the last flowers fade.
If an older plant doesn’t produce many flowers, it can be revived by pruning off 1/3 of the stems near ground level. Pruning older stems in late winter along with deadheading is an effective technique for this plant.
Aphids can sometimes severely infest new growth and cause leaf yellowing or stunting. The waste of these pests, called honeydew, can attract sooty mold. While this fungus may not directly attack the plant, it can block the foliage from getting sunlight. Ants also like honeydew, with some species grooming aphids to stimulate more production and defend aphids from predators and parasites. Aphids can be sprayed off the plant with water or using insecticidal soap.
Powdery mildew can also be a problem when the foliage is wet. Always water the soil to avoid water from contacting the foliage. Watering the plant early will allow any wet foliage to dry during the day. Treating plants infected by this fungus involves removing any foliage or stems that are infected. Severe infection might mean removing large portions of the plant. Neem oil will help kill any traces of the fungus remaining on the plant.